Green Tea Polyphenols and Human Skin

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Green Tea Polyphenols and Human Skin

A position paper for people who have increased photoaging and are searching for a way to improve their skin

Kristen Poppell

Fall 2005

A paper for Reader’s Digest magazine

Skin is one of the most important features of your body. It is composed of thick layers of tissues that protect our bodies in many different ways. It protects us from harsh environmental factors, toxins in the air, injuries, etc. People like you and I are constantly trying to find more effective ways to protect and improve the overall quality of our skin. Whether you want to reduce wrinkles for aesthetic reasons or just want to protect your skin from harmful UV rays, everyone has a different objective for desiring healthy skin. Due to high rates of melanoma (1 in 84 people), I have become more interested in finding ways to protect my own skin. Researchers have just begun to study the positive effects green tea, specifically the phenols found in green tea, can have on your skin. If in later years researchers conclude that green tea polyphenols do in fact have a photoprotective effect on human skin, it is possible that we could see a decrease in skin cancer rates. However, because this is an unresolved issue, green tea polyphenols are not used as the mainstream treatment against UV-radiation. Clinical studies continue to be performed in order to test the effects green tea polyphenols have on your skin.

This paper is based on fourteen studies performed in the past six years on green tea polyphenols and its photoprotective effects on skin. Ten out of the fourteen are actual clinical studies and four are reviews. Approximately six out of the ten clinical studies used a population consisting of either humans or human skin cells and the other four studies used laboratory animal as the treatment group. Nine of my clinical studies support the evidence that green tea polyphenols do in fact have a positive effect on human skin. One study reached the opposite conclusion concerning green tea polyphenols and its effects on the skin. Oral consumption as well as topical treatments of green tea components were administered to subjects in the study. Refer to Table: 1 to see the breakdown of all the different studies used in this paper.

This review argues the issue of green tea polyphenols and the photoprotective effects it may have on your skin. As a position paper I will use all resources available to me in order to reach the best possible conclusion concerning this issue. I am writing this paper to inform you that there may be another way to improve the overall quality of your skin in addition to sunscreen and cosmetic topical creams. I will discuss this issue in terms of how the green tea polyphenols play a role in keratinocyte growth or inhibition of growth when your skin is exposed to UV-A and UV-B radiation. I will also talk about the effects it may have when orally administered and/or used as a topical treatment in everyday life (i.e., not exposed to specific intensities UV-light in a controlled environment). Lastly, I will discuss the amount of sunburn cells present in the skin when exposed to UV-light. This amount should decrease when treated with green tea polyphenols. The skin will be tested to see how resilient it is when exposed to UV- light.

Human skin is broken down into three major divisions: the epidermis (outer layer), the dermis (middle layer), and the hypodermis (inner-most layer). See Illustration: 1 for further explanation. When your skin is exposed to UV- light there is a breakdown of collage and elastin fibers. These two components are located in the epidermis and dermis of your skin. Wrinkles, roughness, dryness, etc. begin to take form when there is a breakdown of collagen and elastin fibers in the dermis and epidermis. Wrinkles, roughness, etc. are the symptoms of photoaging. UV-induced oxidative stress acts in proportion to cause photoaging (Fisher, 2002). Keratinocytes are skin cells that are also damaged during UV-exposure. However, if keratinocytes continue to grow under UV-exposure this could lead to a decrease in photoaging. An increase in keratinocyte growth reduces the damage done to the skin when exposed to UV-light. For example, an increase in keratinocytes can cause a reduction of dryness on the epidermal layer and an increase in elastin fibers on the dermal level, which in turn can result in a decrease of wrinkles. Erythema is another important factor to measure when talking about UV-exposure and photoaging. Erythema is described as the number of “sunburn cells” present in skin after the exposure. After spending some time in the sun you want a low number of sunburn cells because a high number contributes to photoaging. For example, if you spend a lot of time in the sun and you do not wear sunscreen your erythema index is going to be very high, causing more wrinkles, dryness, etc. However, if you use sunscreen while you are spending some time in the sun, your erythema index is going to be a lot lower, and that is what you want. Therefore, since green tea polyphenols (GTP) are an antioxidant, many researchers have tested the effects of GTP’s on human skin and some have found positive results. Green tea polyphenols are made up of four different components (-)-epigallocatechin-3-gallate) EGCG, EGC, ECG, and EC. These components are sometimes referred to as green tea extracts (GTE). EGCG is the most commonly tested phenol because it is the most abundant green tea phenols. The polyphenols in green tea have been shown to increase keratinocyte growth as well as decrease your erythema index, which would in turn serve as a photoprotective device for your skin.

Previous studies show conflicting data concerning green tea polyphenols and their effects on either keratinocytes and/or sunburn index. When I compare previous studies, it is apparent that there is conflicting data. In Chiu Annie E., Joanna L. Chan, Dale G. Kern, Sabine Kohler, Wingfield Rehmus, and Alexa Kimball’s (2005) study we can see that out of the 40 women who participated in the experiment, when a 10% green tea topical cream was used in addition to an oral supplement of 300 mg twice a day, there were no results found supporting the idea that green tea polyphenols had a photoprotective effect on the subjects’ skin. (Refer to Figure: 1) However, Chung JH, Han JH, Eun Hwang, Jin Seo, Kwang Cho, Kyu Kim, Jai Youn, and Hee Eun’s (2003) study illustrates the opposite conclusion. The treatment group consisted of 5 elderly men whose treatment consisted of a 10% topical application of EGCG. Chung et al., (2003) found a significant increase in the number of keratinocytes in the treatment group when compared to the control group. Lastly, conflicting data occurred within Elmets, CA, Divya Singh, Karen Tubesing, Mary Matsui, Santosh Katiyar, and Hassan Mukhtar’ s (2001) study, when measuring green tea polyphenols as well as the different components of the phenols. For example, his study consisted of a mixed population of men and women ranging from 18 to 50 years old. They were administered a 5% concentration of GTP, EGCG, EGC, EC, and ECG and subjects were then exposed to UV-light. Data shows mixed results. For example, a 5% concentration of GTP produced a 2% sunburn index, while the EGC component produced an 8% sunburn index. These are just a few examples of why this topic is unresolved and needs to be analyzed further. All studies mentioned above as well as many others are shown in Table: 1 in order to show that there is conflicting data concerning green tea polyphenols and its effects on skin.

I am supporting the idea that green tea polyphenols do have a photoprotective effect on human skin. I chose to support this side of the evidence because the trials performed within each study are highly controlled. Meaning, the subjects who participated as well as the environments they were exposed to were closely monitored. The first method of control was that subjects were administered specific doses of green tea polyphenols, or some extract of, everyday at a given time. Another method of control was that the subjects were exposed to UV-light. The most common source of light used was UV-A because that is where most photoaging occurs. And lastly, I obtained much more evidence in support of the idea that green tea polyphenols have a photoprotective effect on the skin than I found evidence opposing the idea.

My first reason for supporting the conclusion that green tea polyphenols have a photoprotective effect on human skin is the level of control used in the environment. I found consistent and similar results in studies where the environments were highly controlled. A “highly controlled environment,” in this case, is defined as subjects and/or human cells who have been treated with GTP and later were exposed to UV-light. In these studies, human volunteers and/or human skin cells were obtained and treated with green tea polyphenols, either orally or topically. After subjects were administered GTP they were exposed to a specific light source; in most cases UV-A light was used. By using a specific light source researchers were able to control the exact amount of UV-light the participant had received. This is an important measure of control because researchers were then able to analyze the effects GTP had on the skin cells when exposed to direct UV-light at a specific time. Highly controlled studies provide us with data illustrating the positive photoprotective effects green tea polyphenols can have on your skin when exposed to UV-A light (Refer to Figure: 2a and 2b). When researchers measured the epidermal thickness of subjects in the study, they were testing the effect GTP had on keratinocyte growth. In the studies I analyzed, I discovered strong supporting data that an application of GTP administered in a highly controlled environment does have a positive effect on epidermal thickness. For example, in the Chung et al., (2003) study, data shows that a topical application of 10% EGCG significantly increased epidermal thickness by 70%. Another example of a highly controlled study that produced positive outcomes was Zhao et. al., (1999). This study measured the effects GTP had on the erythema index. Data shows that when the participants were exposed to UV-A light there was very noticeable delay of erythema formation (only in subjects who had been treated with GTP). Evidence shows that in all studies that provided a high level of control for their subjects, the GTP or EGCG was effective in either reducing the erythema index or increasing keratinocyte growth. Refer to Illustration: 2 to see an example what results can be achieved when GTP is given and then exposed to direct UV light.

However, my counterargument suggests that green tea polyphenols do not have a photoprotective effect on skin. My counterargument contains studies that are loosely controlled. This means that subjects were not placed under UV-A after they were treated with GTP. In the weaker study, lower level of control, subjects were administered GTP, but then they were not directly exposed to a UV light source. They just continued with their daily activities. Chiu’s et al., 2005 study is an example of a loosely controlled environment and how it affects the results found. In this study, topical cream with a 10% concentration of green tea and a 300mg oral supplement of green tea taken twice daily or a placebo were given out to forty subjects. They were told to administer the green tea to themselves for 8 weeks. After the 8 weeks were up histologic results show no improvement in epidermal thickness. In the placebo group (n=22) data shows a 0.09 improvement and in the treatment group (n=15) data shows a 0.00 increase in epidermal thickness. Due to the relatively high doses of GTP tested in my counterargument it may be considered a strength, but because there is such a lack of control with UV-light, the dose becomes insignificant. (Refer to Table: 2)

My second reason for supporting the idea that green tea polyphenols do have a photoprotective effect on the skin was how the GTP was administered. In the highly controlled studies researchers administered the GTP to the subjects and monitored them throughout the time they were being studied. More specifically, keratinocytes were also obtained from different individuals (laboratory animals) and were injected with GTP. Hsu’s et. al., (2003) study produced positive results by monitoring their dosage of EGCG administered to keratinocytes. (This is shown in Illustration: 3) Researchers were able to control how much GTP a participant was supposed to topically apply or orally ingest at a given time. This form of control does not leave any room for the subject to make an error when administering the green tea polyphenols. One example of this form of control is present in Elmets et. al., (2000). In this study, a specific amount of 0.2 mL of GTP in concentrations ranging from 1% to 10% was applied to the backs of six volunteers. Results from this study found that different concentrations of green tea polyphenols decrease erythema index in treated subjects. Although I only discussed a couple of studies where the administration of GTP was highly monitored. Refer to Table: 1 for more studies where this method was used. Not all of the studies had high levels of control when it came to the administration of green tea phenols.

The evidence for my counterargument shows that subjects were not monitored closely when they administered the topical application and oral supplement of green tea. This is considered to be a weaker study because there is a lot of room for error on the participant’s part. It is possible that some subjects could have made mistakes while taking the green tea. For example, they could have forgotten to take the oral supplement one day, they could have forgotten to apply the topical cream, or they could have administered the treatment at the wrong time. Whatever the case may be, we can conclude that a loosely monitored environment is not a strong method of control for determining the effects green tea polyphenols may have on human skin. For example, in Chiu’s et. al., (2003) study, results show that GTP had no effect on keratinocyte growth (erythema was not measured in this specific study). Fairly high doses of GTP were used in this study, but as stated before because the subjects were not administered the treatment in the most controlled way, the dose becomes insignificant

My third reason for supporting the idea that green tea polyphenols have a protective effect on the skin was that more evidence was found. Overall, there were more studies in support of my position than there were opposing it. Refer to Table: 1 for evidence. Evidence from the table will show that studies in support of my position are stronger because they are more highly controlled than the others. Therefore, I obtained a larger number of highly controlled studies than I did loosely controlled ones.

I only found one study that provided me with the evidence that green tea polyphenols do not have a photoprotective effect on skin. This counterargument is strong in that it directly contradicts my position, but there were just not enough strong studies (i.e., highly controlled) showing evidence that green tea polyphenols had no effect on the skin. There was only one study that supported my counterargument. It was enough evidence to counter act my own position because this study included the largest number of individual participants. However, this study was so loosely controlled, that it made all of this evidence weak.

Hopefully in the future green tea polyphenols will be used as over the counter product that can help improve the quality of your skin. After comparing several previous studies, I think it is very clear that GTP can be used as a photoprotective device against photoaging. The reasons why I have reached this conclusion are as follows: I had more evidence supporting the idea that green tea polyphenols have a photoprotective effect on skin, the evidence in my stronger studies used a high level of control for the environment (UV), and lastly the evidence in my stronger studies used a high level of control for the administration of GTP. When all three of these factors are taken into consideration it is easy to see why my position is the strongest argument. However, like all arguments, my position has flaws. A major flaw of my position was that, in all the papers, different concentrations were given in different units of measurement. This made it somewhat difficult to compare the exact results in one study to the exact results in another. In the future, multiple studies performed should have only high levels of control (i.e. strict control of UV and administration of treatment). Future studies should also use the same units for measuring green tea polyphenols. From this review you should have learned that green tea polyphenols, when administered in a highly controlled environment, could increase your keratinocyte growth and decrease your erythema index. In turn, this will cause a reduction in photoaging.

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